Makefile: don't run 'go list ./...' on each invocation of 'make'
Makefile: don't run 'go list ./...' on each invocation of 'make'

When run in a VM with the Cilium repo mounted over vboxsf or 9p,
`make foo` takes a significant amount of time to start running its first task.
It appears that `go list` is run unconditionally on startup.

This commit moves the only necessary use of GOPKGS_EVAL to occur within the
cscope.files target so this is no longer the case.

Signed-off-by: Timo Beckers <98c2d5a1e48c998bd9ba9dbc53d6857beae1c9bd@isovalent.com>

cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium